Methyl-Substituted Biphenyl Compounds, Their Production and Their Use in the Manufacture of Plasticizers

ABSTRACT

In a process for producing a methyl-substituted biphenyl compound, at least one methyl-substituted cyclohexylbenzene compound of the formula: 
     
       
         
         
             
             
         
       
     
     wherein each of m and n is independently an integer from 1 to 3, is contacted with a dehydrogenation catalyst under conditions effective to produce a dehydrogenation reaction product comprising at least one methyl-substituted biphenyl compound. The dehydrogenation catalyst comprises an element or compound thereof from Group 10 of the Periodic Table of Elements deposited on a refractory support, such as alumina.

PRIORITY

This application claims the benefit of and priority to ProvisionalApplication No. 61/781,728, filed Mar. 14, 2013.

FIELD

The disclosure relates to methyl-substituted biphenyl compounds, theirproduction and their use in the manufacture of plasticizers.

BACKGROUND

Plasticizers are incorporated into a resin (usually a plastic orelastomer) to increase the flexibility, workability, or distensibilityof the resin. The largest use of plasticizers is in the production of“plasticized” or flexible polyvinyl chloride (PVC) is products. Typicaluses of plasticized PVC include films, sheets, tubing, coated fabrics,wire and cable insulation and jacketing, toys, flooring materials suchas vinyl sheet flooring or vinyl floor tiles, adhesives, sealants, inks,and medical products such as blood bags and tubing, and the like.

Other polymer systems that use small amounts of plasticizers includepolyvinyl butyral, acrylic polymers, nylon, polyolefins, polyurethanes,and certain fluoroplastics. Plasticizers can also be used with rubber(although often these materials fall under the definition of extendersfor rubber rather than plasticizers). A listing of the majorplasticizers and their compatibilities with different polymer systems isprovided in “Plasticizers,” A. D. Godwin, in Applied Polymer Science21st Century, edited by C. D. Craver and C. E. Carraher, Elsevier(2000); pp. 157-175.

The most important chemical class of plasticizers is phthalic acidesters, which accounted for about 84% worldwide of PVC plasticizer usagein 2009. However, there is an effort to decrease the use of phthalateesters as plasticizers in PVC, particularly in end uses where theproduct contacts food, such as bottle cap liners and sealants, medicaland food films, or for medical examination gloves, blood bags, and IVdelivery systems, flexible tubing, or for toys, and the like. As aresult, there is a need for non-phthalate, mono- or diesterplasticizers, particularly oxo-ester plasticizers, that can be made fromlow cost feeds and employ few manufacturing steps in order to havecomparable economics with their phthalate counterparts. For these andmost other uses of plasticized polymer systems, however, a successfulsubstitute for phthalate esters has not yet been found.

One such suggested substitute for phthalates are esters based oncyclohexanoic acid. In the late 1990's and early 2000's, variouscompositions based on cyclohexanoate, cyclohexanedioates, andcyclohexanepolyoate esters were said to be useful for a range of goodsfrom semi-rigid to highly flexible materials. See, for instance, WO99/32427, WO 2004/046078, WO 2003/029339, U.S. Patent Publication No.2006-0247461, and U.S. Pat. No. 7,297,738.

Other suggested substitutes include esters based on benzoic acid (see,for instance, U.S. Pat. No. 6,740,254) and polyketones, such asdescribed in U.S. Pat. No. 6,777,514; and U.S. Patent Publication No.2008-0242895. Epoxidized soybean oil, which has much longer alkyl groups(C₁₆ to C₁₈), has been tried as a plasticizer, but is generally used asa PVC stabilizer. Stabilizers are used in much lower concentrations thanplasticizers. U.S. Patent Publication No. 2010-0159177 disclosestriglycerides with a total carbon number of the is triester groupsbetween 20 and 25, produced by esterification of glycerol with acombination of acids derived from the hydroformylation and subsequentoxidation of C₃ to C₉ olefins, having excellent compatibility with awide variety of resins and that can be made with a high throughput.

Typically, the best that has been achieved with substitution of thephthalate ester with an alternative material is a flexible PVC articlehaving either reduced performance or poorer processability. Thus,existing efforts to make phthalate-free plasticizer systems for PVC havenot proven to be entirely satisfactory, and so this is still an area ofintense research.

For example, in an article entitled “Esters of diphenic acid and theirplasticizing properties”, Kulev et al., Izvestiya TomskogoPolitekhnicheskogo Instituta (1961) 111, disclose that diisoamyldiphenate, bis(2-ethylhexyl)diphenate and mixed heptyl, octyl and nonyldiphenates can be prepared by esterification of diphenic acid, andallege that the resultant esters are useful as plasticizers for vinylchloride. Similarly, in an article entitled “Synthesis of dialkyldiphenates and their properties”, Shioda et al., Yuki Gosei KagakuKyokaishi (1959), 17, disclose that dialkyl diphenates of C₁ to C₈alcohols, said to be useful as plasticizers for poly(vinyl chloride),can be formed by converting diphenic acid to diphenic anhydride andesterifying the diphenic anhydride. However, since these processesinvolve esterification of diphenic acid or anhydride, they necessarilyresult in 2,2′-substituted diesters of diphenic acid. Generally, suchdiesters having substitution on the 2-carbons have proven to be toovolatile for use as plasticizers.

An alternative method of producing dialkyl diphenate esters having anincreased proportion of the less volatile 3,3′, 3,4′ and 4,4′ diestershas now been developed. In particular, it has been found that dimethylbiphenyl compounds containing significant amounts of the 3,3′-dimethyl,the 3,4′-dimethyl and the 4,4′-dimethyl isomers can be economicallyproduced by hydroalkylation of toluene and/or xylene followed bycatalyst dehydrogenation of the resulting (methylcyclohexyl)tolueneand/or (dimethylcyclohexyl)xylene product. The resultant mixture canthen be used as a precursor in the production of biphenylester-basedplasticizers by, for example, oxidizing the methyl-substituted biphenylcompounds to convert at least one of the methyl groups to a carboxylicacid group and then esterifying the carboxylic acid group(s) with analcohol, such as an oxo alcohol. One important step in this overallprocess is the dehydrogenation reaction and, in particular, it has nowbeen found that an effective catalyst for the dehydrogenation reactionis a Group 10 metal dispersed on a refractory support. In addition, ithas been found that the dehydrogenation catalyst exhibits improvesactivity and stability when an acidic inorganic is oxide material, suchas alumina, is employed as the refractory support. The improved activityprovided by such an acidic support allows the amount of expensive Group10 metal in the catalyst to be reduced.

SUMMARY

Accordingly, in one aspect, the present disclosure relates to a processfor producing a methyl-substituted biphenyl compound, the processcomprising:

(a) contacting at least one methyl-substituted cyclohexylbenzenecompound of the formula:

with a dehydrogenation catalyst under conditions effective to produce adehydrogenation reaction product comprising at least onemethyl-substituted biphenyl compound wherein each of m and n isindependently an integer from 1 to 3 and wherein the dehydrogenationcatalyst comprises an element or compound thereof from Group 10 of thePeriodic Table of Elements dispersed on a refractory support.

In a further aspect, the present disclosure relates to a process forproducing methyl-substituted biphenyl compounds, the process comprising:

(a) contacting a feed comprising at least one aromatic hydrocarbonselected from the group consisting of toluene, xylene and mixturesthereof with hydrogen in the presence of a hydroalkylation catalystunder conditions effective to produce a hydroalkylation reaction productcomprising (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes; and

(b) dehydrogenating at least part of the hydroalkylation reactionproduct in the presence of a dehydrogenation catalyst under conditionseffective to produce a dehydrogenation reaction product comprising amixture of methyl-substituted biphenyl compounds, wherein thedehydrogenation catalyst comprises an element or compound thereof fromGroup 10 of the Periodic Table of Elements dispersed on a refractorysupport.

In yet a further aspect, the present disclosure relates to a process forproducing biphenyl esters, the process comprising:

(a) contacting a feed comprising at least one aromatic hydrocarbonselected from the group consisting of toluene, xylene and mixturesthereof with hydrogen in the presence of a hydroalkylation catalystunder conditions effective to produce a hydroalkylation reaction productcomprising (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes;

(b) dehydrogenating at least part of the hydroalkylation reactionproduct in the is presence of a dehydrogenation catalyst underconditions effective to produce a dehydrogenation reaction productcomprising a mixture of methyl-substituted biphenyl compounds, whereinthe dehydrogenation catalyst comprises an element or compound thereoffrom Group 10 of the Periodic Table of Elements dispersed on arefractory support;

(c) contacting at least part of the dehydrogenation reaction productwith an oxygen source under conditions effective to convert at leastpart of the methyl-substituted biphenyl compounds to biphenyl carboxylicacids; and

(d) reacting the biphenyl carboxylic acids with one or more C₄ to C₁₄alcohols under conditions effective to produce biphenyl esters.

In one embodiment, the dehydrogenation catalyst comprises a refractorysupport of has one or more of the following properties:

(i) an alpha value between 0.1 to 10;

(ii) a combined Bronsted and Lewis acid activity from 0.1 to 0.5 mmol/gmof the dehydrogenation catalyst; and

(iii) a temperature programmed ammonia adsorption from 0.1 to 1 mmol/gmof the dehydrogenation catalyst.

In one embodiment, the dehydrogenation catalyst contains less than 1 wt% of said element or compound thereof from Group 10 of the PeriodicTable of Elements.

In one embodiment, the dehydrogenation catalyst further comprises tin ora compound thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of conversion against time on stream for thealumina-supported catalyst of Example 5 and the carbon-supportedcatalyst of Example 3 in the dehydrogenation testing of Example 9.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Described herein is a process for producing methyl substituted biphenylcompounds useful as precursors in the manufacture of biphenyl esterplasticizers. As discussed below, the process involves the catalytichydroalkylation of toluene and/or xylene to produce methyl-substitutedcyclohexylbenzene compounds followed by the dehydrogenation of at leastpart of the hydroalkylation reaction product in the presence of adehydrogenation catalyst. The dehydrogenation catalyst comprises anelement or compound thereof from Group 10 of the Periodic Table ofElements deposited on a refractory support. In one embodiment, it isfound that the activity and stability of the dehydrogenation catalystcan be significantly improved if the refractory support is selected tohave certain acidic properties discussed in more detail in the ensuingdescription. In addition, the improvement activity allows the amount ofexpensive Group 10 metal in the catalyst to be reduced without impairingthe dehydrogenation performance of the catalyst.

As used herein, the numbering scheme for the Periodic Table Groups is asdisclosed in Chemical and Engineering News, 63(5), 27 (1985).

As used herein, the term “C_(n)” hydrocarbon wherein n is a positiveinteger, e.g., 1, 2, 3, 4, etc, means a hydrocarbon having n number ofcarbon atom(s) per molecule. The term “C_(n)+” hydrocarbon wherein n isa positive integer, e.g., 1, 2, 3, 4, etc, as used herein, means ahydrocarbon having at least n number of carbon atom(s) per molecule. Theterm “C_(c)−” hydrocarbon wherein n is a positive integer, e.g., 1, 2,3, 4, etc., used herein, means a hydrocarbon having no more than nnumber of carbon atom(s) per molecule.

Hydroalkylation of Toluene and/or Xylene

Hydroalkylation is a two-stage catalytic reaction in which an aromaticcompound is partially hydrogenated to produce a cyclic olefin, whichthen reacts, in situ, with the aromatic compound to produce acycloalkylaromatic product. In the present process, the aromatic feedcomprises toluene and/or xylene and the cycloalkylaromatic productcomprises a mixture of (methylcyclohexyl)toluene and/or(dimethylcyclohexyl)xylene isomers. In the case of toluene, the desiredreaction may be summarized as follows:

Among the competing reactions is further hydrogenation of the cyclicolefin intermediate and/or the cycloalkylaromatic product to producefully saturated rings. In the case of toluene as the hydroalkylationfeed, further hydrogenation can produce methylcyclohexane anddimethylbicyclohexane compounds. Although these by-products can beconverted back to feed (toluene) and to the product((methylcyclohexyl)toluene and dimethylbiphenyl) via dehydrogenation,this involves an endothermic reaction requiring high temperatures (>375°C.) to obtain high conversion. This not only makes the reaction costlybut can also lead to further by-product formation and hence yield loss.It is therefore desirable to employ a hydroalkylation catalyst thatexhibits low selectivity towards the production of fully saturatedrings.

Another competing reaction is dialkylation in which the(methylcyclohexyl)toluene product reacts with further methylcyclohexeneto produce di(methylcyclohexyl)toluene according to the followingreactions:

Again this dialkylated by-product can be converted back to(methylcyclohexyl)toluene, in this case by transalkylation. However,this process requires the use of an acid catalyst at temperatures above160° C. and can lead to the production of additional by-products, suchas di(methylcyclopentyl)toluenes, cyclohexylxylenes andcyclohexylbenzene. It is therefore desirable to employ a hydroalkylationcatalyst that exhibits low selectivity towardsdi(methylcyclohexyl)toluene and other heavy by-products.

The catalyst employed in the hydroalkylation reaction is a bifunctionalcatalyst comprising a hydrogenation component and a solid acidalkylation component, typically a molecular sieve. The catalyst may alsoinclude a binder such as clay, silica and/or metal oxides. The lattermay be either naturally occurring or in the form of gelatinousprecipitates or gels including mixtures of silica and metal oxides.Naturally occurring clays which can be used as a binder include those ofthe montmorillonite and kaolin families, which families include thesubbentonites and the kaolins commonly known as Dixie, McNamee, Georgiaand Florida clays or others in which the main mineral constituent ishalloysite, kaolinite, dickite, nacrite or anauxite. Such clays can beused in the raw state as originally mined or initially subjected tocalcination, acid treatment or chemical modification. Suitable metaloxide binders include silica, alumina, zirconia, titania,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia.

Any known hydrogenation metal or compound thereof can be employed as thehydrogenation component of the catalyst, although suitable metalsinclude palladium, ruthenium, nickel, zinc, tin, and cobalt, withpalladium being particularly advantageous. In certain embodiments, theamount of hydrogenation metal present in the catalyst is between about0.05 and about 10 wt %, such as between about 0.1 and about 5 wt %, ofthe catalyst.

In one embodiment, the solid acid alkylation component comprises a largepore molecular sieve having a Constraint Index (as defined in U.S. Pat.No. 4,016,218) less than 2. Suitable large pore molecular sieves includezeolite beta, zeolite Y, Ultrastable Y (USY), Dealuminized Y (Deal Y),mordenite, ZSM-3, ZSM-4, ZSM-18, and ZSM-20. Zeolite ZSM-14 is describedin U.S. Pat. No. 3,923,636. Zeolite ZSM-20 is described in U.S. Pat. No.3,972,983. Zeolite Beta is described in U.S. Pat. No. 3,308,069, and Re.No. 28,341. Low sodium Ultrastable Y molecular sieve (USY) is describedin U.S. Pat. Nos. 3,293,192 and 3,449,070. Dealuminized Y zeolite (DealY) may be prepared by the method found in U.S. Pat. No. 3,442,795.Zeolite UHP-Y is described in U.S. Pat. No. 4,401,556. Mordenite is anaturally occurring material but is also available in synthetic forms,such as TEA-mordenite (i.e., synthetic mordenite prepared from areaction mixture comprising a tetraethylammonium directing agent).TEA-mordenite is disclosed in U.S. Pat. Nos. 3,766,093 and 3,894,104.

In another, more preferred embodiment, the solid acid alkylationcomponent comprises a molecular sieve of the MCM-22 family. The term“MCM-22 family material” (or “material of the MCM-22 family” or“molecular sieve of the MCM-22 family”), as used herein, includes one ormore of:

-   -   molecular sieves made from a common first degree crystalline        building block unit cell, which unit cell has the MWW framework        topology. (A unit cell is a spatial arrangement of atoms which        if tiled in three-dimensional space describes the crystal        structure. Such crystal structures are discussed in the “Atlas        of Zeolite Framework Types”, Fifth edition, 2001, the entire        content of which is incorporated as reference);    -   molecular sieves made from a common second degree building        block, being a 2-dimensional tiling of such MWW framework        topology unit cells, forming a monolayer of one unit cell        thickness, preferably one c-unit cell thickness;    -   molecular sieves made from common second degree building blocks,        being layers of one or more than one unit cell thickness,        wherein the layer of more than one unit cell thickness is made        from stacking, packing, or binding at least two monolayers of        one unit cell thickness. The stacking of such second degree        building blocks can be in a regular fashion, an irregular        fashion, a random fashion, or any combination thereof; and    -   molecular sieves made by any regular or random 2-dimensional or        3-dimensional combination of unit cells having the MWW framework        topology.

Molecular sieves of MCM-22 family generally have an X-ray diffractionpattern including d-spacing maxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and3.42±0.07 Angstrom. The X-ray diffraction data used to characterize thematerial are obtained by standard techniques using the K-alpha doubletof copper as the incident radiation and a diffractometer equipped with ascintillation counter and associated computer as the collection system.Molecular sieves of MCM-22 family include MCM-22 (described in U.S. Pat.No. 4,954,325), PSH-3 (described in U.S. Pat. No. 4,439,409), SSZ-25(described in U.S. Pat. No. 4,826,667), ERB-1 (described in EuropeanPatent No. 0293032), ITQ-1 (described in U.S. Pat. No. 6,077,498), ITQ-2(described in International Patent Publication No. WO97/17290), MCM-36(described in U.S. Pat. No. 5,250,277), MCM-49 (described in U.S. Pat.No. 5,236,575), MCM-56 (described in U.S. Pat. No. 5,362,697) andmixtures thereof.

In addition to the toluene and/or xylene and hydrogen, a diluent, whichis substantially inert under hydroalkylation conditions, may be suppliedto the hydroalkylation reaction. In certain embodiments, the diluent isa hydrocarbon, in which the desired cycloalkylaromatic product issoluble, such as a straight chain paraffinic hydrocarbon, a branchedchain paraffinic hydrocarbon, and/or a cyclic paraffinic hydrocarbon.Examples of suitable diluents are decane and cyclohexane. Although theamount of diluent is not narrowly defined, desirably the diluent isadded in an amount such that the weight ratio of the diluent to thearomatic compound is at least 1:100; for example at least 1:10, but nomore than 10:1, desirably no more than 4:1.

In one embodiment, the aromatic feed to the hydroalkylation reactionalso includes benzene and/or one or more alkylbenzenes different fromtoluene and xylene. Suitable alkylbenzenes may have one or more alkylgroups with up to 4 carbon atoms and include, by way of example,ethylbenzene, cumene, and unseparated C₆-C₈ or C₇-C₈ or C₇-C₉ streams.

The hydroalkylation reaction can be conducted in a wide range of reactorconfigurations including fixed bed, slurry reactors, and/or catalyticdistillation towers. In addition, the hydroalkylation reaction can beconducted in a single reaction zone or in a plurality of reaction zones,in which at least the hydrogen is introduced to the reaction in stages.Suitable reaction temperatures are between about 100° C. and about 400°C., such as between about 125° C. and about 250° C., while suitablereaction pressures are between about is 100 and about 7,000 kPa, such asbetween about 500 and about 5,000 kPa. The molar ratio of hydrogen toaromatic feed is typically from about 0.15:1 to about 15:1.

In the present process, it is found that MCM-22 family molecular sievesare particularly active and stable catalysts for the hydroalkylation oftoluene or xylene. In addition, catalysts containing MCM-22 familymolecular sieves exhibit improved selectivity to the 3,3′-dimethyl, the3,4′-dimethyl, the 4,3′-dimethyl and the 4,4′-dimethyl isomers in thehydroalkylation product, while at the same time reducing the formationof fully saturated and heavy by-products. For example, using an MCM-22family molecular sieve with a toluene feed, it is found that thehydroalkylation reaction product may comprise:

-   -   at least 60 wt %, such as at least 70 wt %, for example at least        80 wt % of the 3,3,3,4,4,3 and 4,4-isomers of        (methylcyclohexyl)toluene based on the total weight of all the        (methylcyclohexyl)toluene isomers;    -   less than 30 wt % of methylcyclohexane and less than 2% of        dimethylbicyclohexane compounds;    -   and less than 1 wt % of dialkylated C₂₁+ compounds.

Similarly, with a xylene feed, the hydroalkylation reaction product maycomprise less than 1 wt % of compounds containing in excess of 16 carbonatoms.

By way of illustration, the 3,3,3,4,4,3 and 4,4-isomers of(methylcyclohexyl)toluene are illustrated in formulas F1 to F4,respectively:

In contrast, when the methyl group is located in the 1-position(quaternary carbon) on the cyclohexyl ring, ring isomerization can occurforming (dimethylcyclopentyl)toluene and (ethylcyclopentyl)toluenewhich, on dehydrogenation, will generate diene by-products which aredifficult to separate from the desired product and will also inhibit thesubsequent oxidation reaction. In the oxidation and esterificationsteps, different isomers have different reactivity. Thus, para-isomersare more reactive than meta-isomers which are more reactive thanortho-isomers. Also in the dehydrogenation step, the presence of amethyl group in the 2 position on either the cyclohexyl or phenyl ringis a precursor for the formation of fluorene and methyl fluorene.Fluorene is difficult to separate from the dimethylbiphenyl product andcauses problems in the oxidation step and also in the plasticizersperformance. It is therefore advantageous to minimize the formation ofisomers which have a methyl group in the ortho, 2 and benzylicpositions.

Dehydrogenation of Hydroalkylation Product

The major components of the hydroalkylation reaction effluent are(methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes, unreactedaromatic feed (toluene and/or xylene), fully saturated single ringby-products (methylcyclohexane and dimethylcyclohexane), and somedialkylated C₂₁+ compounds. The unreacted feed and light by-products canreadily be removed from the reaction effluent by, for example,distillation. The unreacted feed can then be recycled to thehydroalkylation reactor, while the saturated by-products can bedehydrogenated to produce additional recyclable feed. In the presentprocess, some or all of the dialkylated C₂₁+ compounds are also removedfrom the hydroalkylation reaction effluent, in the same or a separatedistillation step, so that the feed to the subsequent dehydrogenationstep comprises less than 0.5 wt %, such as less than 0.25 wt %, such asless than 0.1 wt %, even no detectable amount, of the dialkylated C₂₁+compounds.

The remainder of the hydroalkylation reaction effluent, composed mainlyof (methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes, isthen dehydrogenated to produce the corresponding methyl-substitutedbiphenyl compounds. The dehydrogenation is conveniently conducted at atemperature from about 200° C. to about 600° C. and a pressure fromabout 100 kPa to about 3550 kPa (atmospheric to about 500 psig) in thepresence of dehydrogenation catalyst. A suitable dehydrogenationcatalyst comprises one or more is elements or compounds thereof selectedfrom Group 10 of the Periodic Table of Elements, for example platinum,on a refractory support. In one embodiment, the Group 10 element ispresent in amount from 0.1 to 5 wt % of the catalyst. In some cases, thedehydrogenation catalyst may also include tin or a tin compound toimprove the selectivity to the desired methyl-substituted biphenylproduct. In one embodiment, the tin is present in amount from 0.05 to2.5 wt % of the catalyst.

The support employed in the dehydrogenation catalyst is refractory inthe sense that it is capable of withstanding the conditions employed inthe dehydrogenation reaction without physical or chemical changes.Non-limiting examples of suitable refractory support materials include:alumina, silica, silica-alumina, titania, calcium oxide, strontiumoxide, barium oxide, magnesium oxide, carbon, zirconia, diatomaceousearth, lanthanide oxides including cerium oxide, lanthanum oxide,neodynium oxide, yttrium oxide and praesodynium oxide, oxides ofchromium, thorium, uranium, niobium and tantalum, tin oxide, zinc oxide,and aluminum phosphate.

In one embodiment, the refractory support is selected to have one ormore, such as two or more, and desirably all, of the following acidicproperties:

-   -   (i) an alpha value between 0.1 to 10;    -   (ii) a combined Bronsted and Lewis acid activity from 0.1 to 0.5        mmol/gm of the dehydrogenation catalyst; and    -   (iii) a temperature programmed ammonia adsorption from 0.1 to 1        mmol/gm of the dehydrogenation catalyst.

Alpha value is a measure of the cracking activity of an acid catalystand is described in U.S. Pat. No. 3,354,078 and in the Journal ofCatalysis, Vol. 4, p. 527 (1965); Vol. 6, p. 278 (1966); and Vol. 61, p.395 (1980), each incorporated herein by reference as to thatdescription. The experimental conditions of the test used herein includea constant temperature of 538° C. and a variable flow rate as describedin detail in the Journal of Catalysis, Vol. 61, page 395.

The Bronsted and Lewis acid activities of an acidic material can bedetermined from the amount of pyridine adsorbed by the material. Such atest can be conducted by grinding the material and then pressing theground material into a thin self-supporting wafer typically having aweight from 10˜15 mg/cm². The wafer is then placed in an IR transmissioncell equipped with CaF₂ windows and the wafer is pre-calcined in vacuumat 450° C. for 1.5 hr. The adsorption of pyridine is carried out at 250°C. from a glass vial attached to the manifold of the cell. The pyridinepartial pressure is measured by a Baratron is pressure transducer. TheIR bands at 1545 cm⁻¹ and 1450 cm⁻¹ are used for the quantitativeevaluation of Bronsted and Lewis acid sites, respectively. The amount ofpyridium ions and Lewis-bonded pyridine per gram of sample can then becalculated using Beer-Lambert's law according to the formula:

n/m=(A _(i) *Q)/(ε_(i) *m)

where

-   -   A_(i): Integrated absorbance [cm⁻¹]    -   ε_(i): Integrated molar extinction coefficient [cm/μmol]    -   m: mass of wafer [g]    -   Q: Geometric surface area of wafer [cm²].

Values for the integrated molar extinction coefficients were adoptedfrom the literature [C. A. Emeis, J. Catal., 141 (1993) 347] to beε_(B)=1.67 cm/μmol for pyridium ions, and ε_(L)=2.22 cm/μmol forLewis-bonded pyridine.

The temperature programmed ammonia absorption (TPAA) measures the totalnumber of acid sites in a sample via the formation of an adsorptioncomplex with Bronsted or Lewis acid sites. In the tests cited herein,before the ammonia absorption, each sample was calcined in air at 500°C. for 1 hr to remove any absorbed moisture and volatiles. The samplewas cooled down in air to 250° C. Then the system was switched to ahelium stream. Recurrent pulses of 1% NH₃/He were added into the system.The sample with ammonia absorption was weighed in-situ by themicrobalance to determine the TPAA value in mmol of NH₃/gm of thesample. After sample acid sites were saturated with NH₃, the system waspurged with helium stream to remove physical absorbed ammonia. Thesystem was ramped from 250° C. to 500° C. with a ramping rate of 5°C./min to generate a programmed ammonia desorption (TPAD) profile.Temperature programmed ammonia adsorption of an acidic material can bemeasured as follows.

Suitable refractory acidic supports for the dehydrogenation catalystcomprise one or more of alumina, silica-alumina, zirconia, titania, andlanthanide oxides, with alumina being preferred.

Where the dehydrogenation catalyst contains tin, the catalyst may beprepared by impregnating the support with an aqueous solution of asuitable tin compound, such as tin chloride, and/or tin tartrate. Theimpregnated support containing Sn is the dried in air, such as at 120°C. for 4 hrs and, and then calcined, such as at 538° C. in air for 3hrs, to convert the tin to an oxide form. Afterwards, Pt is added toSn-containing support by impregnation with an aqueous solution of asuitable platinum compound, such as (NH₃)₄Pt(NO₃)₂. The sample iscontaining Sn and Pt is dried in air, such as at 120° C. for 4 hrs, andthen calcined, such as at 360° C. in air for 3 hrs.

Particularly using an MCM-22 family-based catalyst for the upstreamhydroalkylation reaction and the dehydrogenation catalyst describedabove, the product of the dehydrogenation step comprisesmethyl-substituted biphenyl compounds in which the concentration of the3,3-, 3,4- and 4,4-dimethyl isomers is at least 50 wt %, such as atleast 60 wt %, for example at least 70 wt % based on the total weight ofmethyl-substituted biphenyl isomers. In addition, the product maycontain less than 10 wt %, such as less than 5 wt %, for example lessthan 3 wt % of methyl biphenyl compounds and less than 5 wt %, such asless than 3 wt %, for example less than 1 wt % of fluorene and methylfluorenes combined.

Production of Biphenyl Esters

The methyl-substituted biphenyl compounds produced by thedehydrogenation reaction can readily be converted ester plasticizers bya process comprising oxidation to produce the corresponding carboxylicacids followed by esterification with an alcohol.

The oxidation can be performed by any process known in the art, such asby reacting the methyl-substituted biphenyl compounds with an oxidant,such as oxygen, ozone or air, or any other oxygen source, such ashydrogen peroxide, in the presence of a catalyst at temperatures from30° C. to 300° C., such as from 60° C. to 200° C. Suitable catalystscomprise Co or Mn or a combination of both metals.

The resulting carboxylic acids can then be esterified to producebiphenyl ester plasticizers by reaction with one or more C₄ to C₁₄alcohols. Suitable esterification conditions are well-known in the artand include, but are not limited to, temperatures of 0-300° C. and thepresence or absence of homogeneous or heterogeneous esterificationcatalysts, such as Lewis or Bronsted acid catalysts. Suitable alcoholsare “oxo-alcohols”, by which is meant an organic alcohol, or mixture oforganic alcohols, which is prepared by hydroformylating an olefin,followed by hydrogenation to form the alcohols. Typically, the olefin isformed by light olefin oligomerization over heterogeneous acidcatalysts, which olefins are readily available from refinery processingoperations. The reaction results in mixtures of longer-chain, branchedolefins, which subsequently form longer chain, branched alcohols, asdescribed in U.S. Pat. No. 6,274,756, incorporated herein by referencein its entirety. Another source of olefins used in the OXO process arethrough the oligomerization of ethylene, producing mixtures ofpredominately straight chain alcohols with lesser amounts of lightlybranched alcohols.

The biphenyl ester plasticizers of the present application find use in anumber of is different polymers, such as vinyl chloride resins,polyesters, polyurethanes, ethylene-vinyl acetate copolymers, rubbers,poly(meth)acrylics and mixtures thereof.

The invention will now be more particularly described with reference tothe accompanying drawings and the following non-limiting Examples.

Example 1 Synthesis of 0.3% Pd/MCM-49 Hydroalkylation Catalyst

80 parts MCM-49 zeolite crystals are combined with 20 partspseudoboehmite alumina, on a calcined dry weight basis. The MCM-49 andpseudoboehmite alumina dry powder is placed in a muller and mixed forabout 10 to 30 minutes. Sufficient water and 0.05% polyvinyl alcohol isadded to the MCM-49 and alumina during the mixing process to produce anextrudable paste. The extrudable paste is formed into a 1/20 inch (0.13cm) quadrulobe extrudate using an extruder and the resulting extrudateis dried at a temperature ranging from 250° F. to 325° F. (120° C. to163° C.). After drying, the dried extrudate is heated to 1000° F. (538°C.) under flowing nitrogen. The extrudate is then cooled to ambienttemperature and humidified with saturated air or steam.

After the humidification, the extrudate is ion exchanged with 0.5 to 1 Nammonium nitrate solution. The ammonium nitrate solution ion exchange isrepeated. The ammonium nitrate exchanged extrudate is then washed withdeionized water to remove residual nitrate prior to calcination in air.After washing the wet extrudate, it is dried. The exchanged and driedextrudate is then calcined in a nitrogen/air mixture to a temperature1000° F. (538° C.). Afterwards, the calcined extrudate is cooled to roomtemperature. The 80% MCM-49, 20% Al₂O₃ extrudate was incipient wetnessimpregnated with a palladium (II) chloride solution (target: 0.30% Pd)and then dried overnight at 121° C. The dried catalyst was calcined inair at the following conditions: 5 volumes air per volume catalyst perminute, ramp from ambient to 538° C. at 1° C./min and hold for 3 hours.

Example 2 Hydroalkylation Catalyst Testing

The catalyst of Example 1 was tested in the hydroalkylation of a toluenefeed using the reactor and process described below.

The reactor comprised a stainless steel tube having an outside diameterof: ⅜ inch (0.95 cm), a length of 20.5 inch (52 cm) and a wall thicknessof 0.35 inch (0.9 cm). A piece of stainless steel tubing having a lengthof 8¾ inch (22 cm) and an outside diameter of: ⅜ inch (0.95 cm) and asimilar length of ¼ inch (0.6 cm) tubing of were used in the bottom ofthe reactor (one inside of the other) as a spacer to position andsupport the catalyst in the isothermal zone of the furnace. A ¼ inch(0.6 cm) plug of glass wool was placed on top of the spacer to keep thecatalyst in place. A ⅛ inch (0.3 cm) stainless steel thermo-well wasplaced in the catalyst bed to monitor temperature throughout thecatalyst bed using a movable thermocouple.

The catalyst was sized to 20/40 sieve mesh or cut to 1:1 length todiameter ratio, dispersed with quartz chips (20/40 mesh) then loadedinto the reactor from the top to a volume of 5.5 cc. The catalyst bedtypically was 15 cm. in length. The remaining void space at the top ofthe reactor was filled with quartz chips, with a ¼ plug of glass woolplaced on top of the catalyst bed being used to separate quartz chipsfrom the catalyst. The reactor was installed in a furnace with thecatalyst bed in the middle of the furnace at a pre-marked isothermalzone. The reactor was then pressure and leak tested typically at 300psig (2170 kPa).

The catalyst was pre-conditioned in situ by heating to 25° C. to 240° C.with H₂ flow at 100 cc/min and holding for 12 hours. A 500 cc ISCOsyringe pump was used to introduce a chemical grade toluene feed to thereactor. The feed was pumped through a vaporizer before flowing throughheated lines to the reactor. A Brooks mass flow controller was used toset the hydrogen flow rate. A Grove “Mity Mite” back pressure controllerwas used to control the reactor pressure typically at 150 psig (1135kPa). GC analyses were taken to verify feed composition. The feed wasthen pumped through the catalyst bed held at the reaction temperature of120° C. to 180° C. at a WHSV of 2 and a pressure of 15-200 psig(204-1480 kPa). The liquid products exiting the reactor flowed throughheated lines routed to two collection pots in series, the first potbeing heated to 60° C. and the second pot cooled with chilled coolant toabout 10° C. Material balances were taken at 12 to 24 hrs intervals.Samples were taken and diluted with 50% ethanol for analysis. An Agilent7890 gas chromatograph with FID detector was used for the analysis. Thenon-condensable gas products were routed to an on line HP 5890 GC.

Example 3 Preparation of 1% Pt/0.15% Sn/SiO₂ Dehydrogenation Catalyst

A 1% Pt/0.15% Sn/SiO₂ catalyst was prepared by incipient wetnessimpregnation, in which a 1/20″ (1.2 mm) quadrulobe silica extrudate wasinitially impregnated with an aqueous solution of tin chloride and thendried in air at 121° C. The resultant tin-containing extrudates werethen impregnated with an aqueous solution of tetraammine Pt nitrate andagain dried in air at 121° C. The resultant product was calcined in airat 350° C. for 3 hours before being used in subsequent catalyst testing.

Example 4 Preparation of 1% Pt/θ-Al₂O₃ Dehydrogenation Catalyst

θ-Al₂O₃ 2.5 mm trilobe extrudates were used as a support for Ptdeposition. The extrudates had a surface area of 126 m²/g, a pore volumeof 0.58 cm³/g, and a pore size of 143 {acute over (Å)}, measured by BETN₂ adsorption. Pt was added to θ-Al₂O₃ support by impregnating with anaqueous solution of (NH₃)₄Pt(NO₃)₂. The Pt metal loading on the supportwas adjusted to 1 wt %. After impregnation, the sample was placed in aglass dish at room temperature for 60 minutes to reach equilibrium, thendried in air at 250° F. (120° C.) for 4 hrs and subsequently calcined ina box furnace at 680° F. (360° C.) in air for 3 hrs. The furnace wasramped at 3° F./minute to the final calcinations temperature and the airflow rate for the calcination was adjusted to 5 volume/volumecatalyst/minute.

Example 5 Preparation of 1% Pt/0.3% Sn/θ-Al₂O₃ Dehydrogenation Catalyst

The catalyst was prepared by sequential impregnations. SnCl₂ was addedto θ-Al₂O₃ support by impregnation of an aqueous solution of tinchloride followed by drying the impregnated support in air at 120° C.for 4 hrs. The Sn metal oxide loading on the θ-Al₂O₃ support as Sn was0.3 wt %. Pt was then added to the Sn-containing Al₂O₃ by impregnationwith an aqueous solution of (NH₃)₄Pt(NO₃)₂ followed by drying dried inair at 120° C. for 4 hrs, and then calcination at 360° C. in air for 3hrs. The Pt metal loading on the support was 1 wt %.

Example 6 Preparation of Pt/Sn/θ-Al₂O₃ Dehydrogenation Catalysts withVarying Metal Loadings

The process of Example 5 was used to produce a series of catalystsamples containing different Pt and Sn loadings on θ-Al₂O₃ extrudates.The Pt and Sn contents are 1% Pt+0.30% Sn/θ-Al₂O₃, 1.5% Pt+0.30%Sn/θ-Al₂O₃, and 2.0% Pt+0.50% Sn/θ-Al₂O₃.

In other tests, tin (II) tartrate hydrate solution was used as areplacement for tin chloride (SnCl₂) solution as the Sn precursorcompound for deposition of Sn on the alumina support.

Example 7 Preparation of 0.3% Pt/γ-Al₂O₃ Dehydrogenation Catalysts withand without 0.15% Sn

γ-Al₂O₃ extrudates, which have surface area of 306 m²/g, pore volume of0.85 cm³/g, and pore size of 73 Å, were also used to support Pt and Sn.The Pt and Sn contents on γ-Al₂O₃ extrudates are 0.3% Pt/γ-Al₂O₃, and0.3% Pt+0.15% Sn/γ-Al₂O₃.

Example 8 Preparation of Pt/Sn/Norit Carbon Extrudate DehydrogenationCatalysts

Norit carbon extrudates were also used to produce Pt-supported andPt/Sn-supported catalysts. The carbon extrudates have a surface area of1491 m²/g, pore volume of 0.73 cm³/g, and pore size centered on 46 Å.The Pt and Sn contents are 1% Pt/C, 1% Pt+0.15% Sn/C. The samplecalcination was carried out in nitrogen atmosphere to prevent isoxidation of carbon extrudates.

Example 9 Dehydrogenation Catalyst Testing

The hydroalkylation product from Example 2 (80% conversion) wasfractionated by distillation. The resulting fraction contained theunreacted toluene feed, 2,3′ dimethylbiphenyl, 2,4′ dimethylbiphenyl,and dimethyl bi(cyclohexane). Samples of this fraction weredehydrogenated over the 1% Pt/0.15% Sn/SiO₂ catalyst from Example 3 andthe 1% Pt/0.3% Sn/θ-Al₂O₃ catalyst from Example 5.

The same reactor and testing protocol as described in Example 2 wereused to perform dehydrogenation tests, except the dehydrogenationcatalyst was pre-conditioned in situ by heating to 375° C. to 460° C.with H₂ flow at 100 cc/min and holding for 2 hours. In addition, in thedehydrogenation tests the catalyst bed was held at the reactiontemperature of 375° C. to 460° C. at a WHSV of 2, a hydrogen tohydrocarbon mole ratio of 2:1 to 5:1 and a pressure of 100 psig (790kPa).

The analysis is done on an Agilent 7890 GC with 150 vial sample tray.

Inlet Temp: 220° C.

Detector Temp: 240° C. (Col+make up=constant)Temp Program: Initial temp 120° C. hold for 15 min., ramp at 2° C./minto 180° C., hold 15 min; ramp at 3° C./min. to 220° C. and hold tillend.Column Flow: 2.25 ml/min. (27 cm/sec); Split mode, Split ratio 100:1Injector: Auto sampler (0.2 μl).

Column Parameters:

Two columns joined to make 120 Meters (coupled with Agilent ultimateunion, deactivated.Column # Front end: Supelco β-Dex 120; 60 m×0.25 mm×0.25 μm film joinedtoColumn #2 back end: γ-Dex 325:60 m×0.25 mm×0.25 μm film.

The results of the dehydrogenation testing are summarized in FIG. 1,from which it will be seen that the alumina-supported catalyst ofExample 5 exhibited higher activity and stability than thesilica-supported catalyst of Example 3.

While various embodiments have been described, it is to be understoodthat further embodiments will be apparent to those skilled in the artand that such embodiments are to be considered within the purview andscope of the appended claims. Such further embodiments include thosedefined in the following paragraphs:

A process for producing a methyl-substituted biphenyl compound, theprocess comprising:

(a) contacting at least one methyl-substituted cyclohexylbenzenecompound of the formula:

with a dehydrogenation catalyst under dehydrogenation conditionseffective to produce a dehydrogenation reaction product comprising atleast one methyl-substituted biphenyl compound wherein each of m and nis independently an integer from 1 to 3, and preferably is 1, andwherein the dehydrogenation catalyst comprises an element or compoundthereof from Group 10 of the Periodic Table of Elements dispersed on arefractory support.

A process for producing methyl-substituted biphenyl compounds, theprocess comprising:

(a) contacting a feed comprising at least one aromatic hydrocarbonselected from the group consisting of toluene, xylene and mixturesthereof with hydrogen in the presence of a hydroalkylation catalystunder conditions effective to produce a hydroalkylation reaction productcomprising (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes; and

(b) dehydrogenating at least part of the hydroalkylation reactionproduct in the presence of a dehydrogenation catalyst underdehydrogenation conditions effective to produce a dehydrogenationreaction product comprising a mixture of methyl-substituted biphenylcompounds, wherein the dehydrogenation catalyst comprises an element orcompound thereof from Group 10 of the Periodic Table of Elementsdispersed on a refractory support.

The process of paragraph [0071], wherein the hydroalkylation catalystcomprises an acidic component and a hydrogenation component.

The process of paragraph [0072], wherein the acidic component of thehydroalkylation catalyst comprises a molecular sieve.

The process of paragraph [0073], wherein the molecular sieve is selectedfrom the group consisting of BEA, FAU and MTW structure type molecularsieves, molecular sieves of the MCM-22 family and mixtures thereof,preferably a molecular sieve of the MCM-22 family.

The process of any one of paragraphs [0072] to [0074], wherein thehydrogenation component of the hydroalkylation catalyst selected fromthe group consisting of palladium, ruthenium, nickel, zinc, tin, cobaltand compounds and mixtures thereof.

The process of any one of paragraphs [0071] to [0075], wherein the ishydroalkylation conditions include a temperature from 100° C. to 400° C.and a pressure from 100 to 7,000 kPa.

The process of any one of paragraphs [0071] to [0076], wherein thearomatic hydrocarbon comprises toluene.

The process of any one of paragraphs [0071] to [0077], wherein the feedto (a) further comprises benzene and/or at least one alkylbenzenedifferent from toluene and xylene.

The process of any one of paragraphs [0070] to [0078], wherein therefractory support has one or more of the following properties:

-   -   (i) an alpha value between 0.1 to 10;    -   (ii) a combined Bronsted and Lewis acid activity from 0.1 to 0.5        mmol/gm of the dehydrogenation catalyst; and    -   (iii) a temperature programmed ammonia adsorption from 0.1 to 1        mmol/gm of the dehydrogenation catalyst.

The process of any one of paragraphs [0070] to [0079], wherein therefractory support comprises alumina.

The process of any one of paragraphs [0070] to [0080], wherein thedehydrogenation catalyst contains less than 1 wt % of said element orcompound thereof from Group 10 of the Periodic Table of Elements.

The process of any one of paragraphs [0070] to [0081], wherein thedehydrogenation catalyst further comprises tin or a compound thereof.

The process of any one of paragraphs [0070] to [0082], wherein thedehydrogenation conditions include a temperature from 200° C. to 600° C.and a pressure from 100 kPa to 3550 kPa (atmospheric to 500 psig).

A process for producing biphenyl esters, the process comprising:

(i) contacting at least part of the methyl-substituted biphenylcompounds produced by the process of any one of paragraphs [0070] to[0083] with an oxygen source under conditions effective to convert atleast part of the methyl-substituted biphenyl compounds to biphenylcarboxylic acids; and

(ii) reacting the biphenyl carboxylic acids with one or more C₄ to C₁₄alcohols under conditions effective to produce biphenyl esters.

This invention further relates to:

1. A process for producing a methyl-substituted biphenyl compound, theprocess comprising: (a) contacting at least one methyl-substitutedcyclohexylbenzene compound of the formula:

with a dehydrogenation catalyst under conditions effective to produce adehydrogenation reaction product comprising at least onemethyl-substituted biphenyl compound wherein each of m and n isindependently an integer from 1 to 3 and wherein the dehydrogenationcatalyst comprises an element or compound thereof from Group 10 of thePeriodic Table of Elements dispersed on a refractory support.2. The process of paragraph 1, wherein each of m and n is 1.3. The process of paragraph 1 or 2, wherein the refractory support hasone or more of the following properties:

-   -   (i) an alpha value between 0.1 to 10;    -   (ii) a combined Bronsted and Lewis acid activity from 0.1 to 0.5        mmol/gm of the dehydrogenation catalyst; and    -   (iii) a temperature programmed ammonia adsorption from 0.1 to 1        mmol/gm of the dehydrogenation catalyst.        4. The process of paragraph 1, 2 or 3, wherein the refractory        support comprises alumina.        5. The process of paragraph 1, 2, 3, or 4 wherein the        dehydrogenation catalyst contains less than 1 wt % of said        element or compound thereof from Group 10 of the Periodic Table        of Elements.        6. The process of paragraph 1, 2, 3, 4, or 5, wherein the        dehydrogenation catalyst further comprises tin or a compound        thereof        7. The process of any of the above paragraphs 1 to 6, wherein        the conditions in (a) include a temperature from about 200° C.        to about 600° C. and a pressure from about 100 kPa to about 3550        kPa (atmospheric to about 500 psig).        8. A process for producing methyl-substituted biphenyl        compounds, the process comprising:

(a) contacting a feed comprising at least one aromatic hydrocarbonselected from the group consisting of toluene, xylene and mixturesthereof with hydrogen in the presence of a hydroalkylation catalystunder conditions effective to produce a hydroalkylation reaction productcomprising (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes; and

(b) dehydrogenating at least part of the hydroalkylation reactionproduct in the presence of a dehydrogenation catalyst under conditionseffective to produce a is dehydrogenation reaction product comprising amixture of methyl-substituted biphenyl compounds, wherein thedehydrogenation catalyst comprises an element or compound thereof fromGroup 10 of the Periodic Table of Elements dispersed on a refractorysupport.

9. The process of paragraph 8, wherein the hydroalkylation catalystcomprises an acidic component and a hydrogenation component.10. The process of paragraph 9, wherein the acidic component of thehydroalkylation catalyst comprises a molecular sieve.11. The process of paragraph 10, wherein the molecular sieve comprises amolecular sieve of the MCM-22 family.12. The process of paragraph 9, 10, or 11 wherein the hydrogenationcomponent of the hydroalkylation catalyst selected from the groupconsisting of palladium, ruthenium, nickel, zinc, tin, cobalt andcompounds and mixtures thereof13. The process of any of paragraphs 8 to 12, wherein thehydroalkylation conditions in the contacting (a) include a temperaturefrom about 100° C. to about 400° C. and a pressure from about 100 toabout 7,000 kPa.14. The process of any of paragraphs 8 to 13, wherein the aromatichydrocarbon comprises toluene.15. The process of any of paragraphs 8 to 14, wherein the feed to (a)further comprises benzene and/or at least one alkylbenzene differentfrom toluene and xylene.16. The process of any of paragraphs 8 to 15, wherein the refractorysupport of the dehydrogenation catalyst has one or more of the followingproperties:

-   -   (i) an alpha value between 0.1 to 10;    -   (ii) a combined Bronsted and Lewis acid activity from 0.1 to 0.5        mmol/gm of the dehydrogenation catalyst; and    -   (iii) a temperature programmed ammonia adsorption from 0.1 to 1        mmol/gm of the dehydrogenation catalyst.        17. The process of paragraph 8 or 9, wherein the refractory        acidic support of the dehydrogenation catalyst comprises alumina        18. The process of paragraph 16, wherein the dehydrogenation        catalyst contains less than 1 wt % of said element or compound        thereof from Group 10 of the Periodic Table of Elements.        19. The process of any of paragraphs 8 to 18, wherein the        dehydrogenation catalyst further comprises tin or a compound        thereof        20. The process of any of paragraphs 8 to 19, wherein the        conditions in (b) include a is temperature from about 200° C. to        about 600° C. and a pressure from about 100 kPa to about 3550        kPa (atmospheric to about 500 psig).        21. A process for producing biphenyl esters, the process        comprising:

(a) contacting a feed comprising at least one aromatic hydrocarbonselected from the group consisting of toluene, xylene and mixturesthereof with hydrogen in the presence of a hydroalkylation catalystunder conditions effective to produce a hydroalkylation reaction productcomprising (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes; and

(b) dehydrogenating at least part of the hydroalkylation reactionproduct in the presence of a dehydrogenation catalyst under conditionseffective to produce a dehydrogenation reaction product comprising amixture of methyl-substituted biphenyl compounds, wherein thedehydrogenation catalyst comprises an element or compound thereof fromGroup 10 of the Periodic Table of Elements dispersed on a refractorysupport;

(c) contacting at least part of the dehydrogenation reaction productwith an oxygen source under conditions effective to convert at leastpart of the methyl-substituted biphenyl compounds to biphenyl carboxylicacids; and

(d) reacting the biphenyl carboxylic acids with one or more C₄ to C₁₄alcohols under conditions effective to produce biphenyl esters.

22. The process of paragraph 21, wherein the hydroalkylation catalystcomprises an acidic component and a hydrogenation component.23. The process of paragraph 21 or 22, wherein the acidic component ofthe hydroalkylation catalyst comprises a molecular sieve of the MCM-22family.24. The process of paragraph 21, 22, or 23, wherein the refractorysupport of the dehydrogenation catalyst has one or more of the followingproperties:

-   -   (i) an alpha value between 0.1 to 10;    -   (ii) a combined Bronsted and Lewis acid activity from 0.1 to 0.5        mmol/gm of the dehydrogenation catalyst; and    -   (iii) a temperature programmed ammonia adsorption from 0.1 to 1        mmol/gm of the dehydrogenation catalyst.        25. The process of paragraph 21, 22, 23 or 24 wherein the        refractory acidic support of the dehydrogenation catalyst        comprises alumina

All documents described herein are incorporated by reference herein,including any priority documents and/or testing procedures to the extentthey are not inconsistent with this text, provided however that anypriority document not named in the initially filed application or filingdocuments is NOT incorporated by reference herein. As is apparent isfrom the foregoing general description and the specific embodiments,while forms of the invention have been illustrated and described,various modifications can be made without departing from the spirit andscope of the invention. Accordingly, it is not intended that theinvention be limited thereby. Likewise, the term “comprising” isconsidered synonymous with the term “including” for purposes ofAustralian law. Likewise whenever a composition, an element or a groupof elements is preceded with the transitional phrase “comprising”, it isunderstood that we also contemplate the same composition or group ofelements with transitional phrases “consisting essentially of”,“consisting of”, “selected from the group of consisting of,” or “is”preceding the recitation of the composition, element, or elements andvice versa.

1. A process for producing a methyl-substituted biphenyl compound, theprocess comprising: (a) contacting at least one methyl-substitutedcyclohexylbenzene compound of the formula:

with a dehydrogenation catalyst under conditions effective to produce adehydrogenation reaction product comprising at least onemethyl-substituted biphenyl compound wherein each of m and n isindependently an integer from 1 to 3 and wherein the dehydrogenationcatalyst comprises an element or compound thereof from Group 10 of thePeriodic Table of Elements dispersed on a refractory support.
 2. Theprocess of claim 1, wherein each of m and n is
 1. 3. The process ofclaim 1, wherein the refractory support has one or more of the followingproperties: (i) an alpha value between 0.1 to 10; (ii) a combinedBronsted and Lewis acid activity from 0.1 to 0.5 mmol/gm of thedehydrogenation catalyst; and (iii) a temperature programmed ammoniaadsorption from 0.1 to 1 mmol/gm of the dehydrogenation catalyst.
 4. Theprocess of claim 1, wherein the refractory support comprises alumina. 5.The process of claim 1, wherein the dehydrogenation catalyst containsless than 1 wt % of said element or compound thereof from Group 10 ofthe Periodic Table of Elements.
 6. The process of claim 1, wherein thedehydrogenation catalyst further comprises tin or a compound thereof. 7.The process of claim 1, wherein the conditions in (a) include atemperature from about 200° C. to about 600° C. and a pressure fromabout 100 kPa to about 3550 kPa (atmospheric to about 500 psig).
 8. Aprocess for producing methyl-substituted biphenyl compounds, the processcomprising: (a) contacting a feed comprising at least one aromatichydrocarbon selected from the group consisting of toluene, xylene andmixtures thereof with hydrogen in the presence of a hydroalkylationcatalyst under conditions effective to produce a hydroalkylationreaction product comprising (methylcyclohexyl)toluenes and/or(dimethylcyclohexyl)xylenes; and (b) dehydrogenating at least part ofthe hydroalkylation reaction product in the presence of adehydrogenation catalyst under conditions effective to produce adehydrogenation reaction product comprising a mixture ofmethyl-substituted biphenyl compounds, wherein the dehydrogenationcatalyst comprises an element or compound thereof from Group 10 of thePeriodic Table of Elements dispersed on a refractory support.
 9. Theprocess of claim 8, wherein the hydroalkylation catalyst comprises anacidic component and a hydrogenation component.
 10. The process of claim9, wherein the acidic component of the hydroalkylation catalystcomprises a molecular sieve.
 11. The process of claim 10, wherein themolecular sieve comprises a molecular sieve of the MCM-22 family. 12.The process of claim 9, wherein the hydrogenation component of thehydroalkylation catalyst selected from the group consisting ofpalladium, ruthenium, nickel, zinc, tin, cobalt and compounds andmixtures thereof.
 13. The process of claim 8, wherein thehydroalkylation conditions in the contacting (a) include a temperaturefrom about 100° C. to about 400° C. and a pressure from about 100 toabout 7,000 kPa.
 14. The process of claim 8, wherein the aromatichydrocarbon comprises toluene.
 15. The process of claim 8, wherein thefeed to (a) further comprises benzene and/or at least one alkylbenzenedifferent from toluene and xylene.
 16. The process of claim 8, whereinthe refractory support of the dehydrogenation catalyst has one or moreof the following properties: (i) an alpha value between 0.1 to 10; (ii)a combined Bronsted and Lewis acid activity from 0.1 to 0.5 mmol/gm ofthe dehydrogenation catalyst; and (iii) a temperature programmed ammoniaadsorption from 0.1 to 1 mmol/gm of the dehydrogenation catalyst. 17.The process of claim 8, wherein the refractory acidic support of thedehydrogenation catalyst comprises alumina.
 18. The process of claim 16,wherein the dehydrogenation catalyst contains less than 1 wt % of saidelement or compound thereof from Group 10 of the Periodic Table ofElements.
 19. The process of claim 8, wherein the dehydrogenationcatalyst further comprises tin or a compound thereof.
 20. The process ofclaim 8, wherein the conditions in (b) include a temperature from about200° C. to about 600° C. and a pressure from about 100 kPa to about 3550kPa (atmospheric to about 500 psig).
 21. A process for producingbiphenyl esters, the process comprising: (a) contacting a feedcomprising at least one aromatic hydrocarbon selected from the groupconsisting of toluene, xylene and mixtures thereof with hydrogen in thepresence of a hydroalkylation catalyst under conditions effective toproduce a hydroalkylation reaction product comprising(methylcyclohexyl)toluenes and/or (dimethylcyclohexyl)xylenes; (b)dehydrogenating at least part of the hydroalkylation reaction product inthe presence of a dehydrogenation catalyst under conditions effective toproduce a dehydrogenation reaction product comprising a mixture ofmethyl-substituted biphenyl compounds, wherein the dehydrogenationcatalyst comprises an element or compound thereof from Group 10 of thePeriodic Table of Elements dispersed on a refractory support; (c)contacting at least part of the dehydrogenation reaction product with anoxygen source under conditions effective to convert at least part of themethyl-substituted biphenyl compounds to biphenyl carboxylic acids; and(d) reacting the biphenyl carboxylic acids with one or more C₄ to C₁₄alcohols under conditions effective to produce biphenyl esters.
 22. Theprocess of claim 21, wherein the hydroalkylation catalyst comprises anacidic component and a hydrogenation component.
 23. The process of claim21, wherein the acidic component of the hydroalkylation catalystcomprises a molecular sieve of the MCM-22 family.
 24. The process ofclaim 21, wherein the refractory support of the dehydrogenation catalysthas one or more of the following properties: (i) an alpha value between0.1 to 10; (ii) a combined Bronsted and Lewis acid activity from 0.1 to0.5 mmol/gm of the dehydrogenation catalyst; and (iii) a temperatureprogrammed ammonia adsorption from 0.1 to 1 mmol/gm of thedehydrogenation catalyst.
 25. The process of claim 21, wherein therefractory acidic support of the dehydrogenation catalyst comprisesalumina.